After witnessing behavior of the regeneration logs, its clear that Vanilla
has had bugs with saving duplicate entities for a while....
Some entities are saved in multiple chunks, and now we are bringing those duplicates
out that use to never surface.
This mode will analyze if the entity appears to be a duplicate (near the other dupe uuid)
and delete the entity instead.
This should reduce regenerations to entities that are nowhere near each other, and
therefore more likely to be subject to real UUID collisions due to our
previous bug, and therefor should survive the chunk load.
ideally this should of never mattered, as it will only
be hit if you teleport out of an unloaded chunk...
But apparently some people are triggering this.
See #1223
Should fix#1280
Citizens hijacks entity map, and im guessing under the right conditions
the result might actually be null during entity creation
Pre the cache patch, the id is looked up on save, so it was fine.
Now, if its null and the save ID is requested, we will try to look
it up again and cache it if found.
Aikar